Cured materials made of a resin composition used in the electrical and electronic industries, such as heat-resistant coating materials and electric insulating materials, for example, interlayer insulation materials for a printed circuit board, building materials, insulating materials for semiconductors, and heat-resistant adhesives are required to have improved heat resistance, and electrical properties, such as a lower dielectric constant and a lower dielectric tangent, and flexibility. In addition, improvements in the storage stability of such resin compositions before curing are desired. In particular, problems have been found to occur in terms of transfer characteristics, such as transfer delays in signals from printed circuit boards and generation of cross-talk due to recent improvements in signal speed and the high frequency of electronic equipment, such as computers. In addition, the resin composition used in a print board is required to provide a cured material having a lower dielectric constant.
Examples of a resin composition which can provide a cured material having excellent heat resistance include a resin composition containing an epoxy resin. Examples of the resin composition include an epoxy resin composition containing an epoxy resin having a weight average molecular weight of less than 35,000, a polyfunctional phenol resin, and an epoxy resin having a weight average molecular weight of 35,000 or more, a curing accelerator, a reducing agent, and a urea compound (for example, see Patent document No. 1). However, this epoxy resin composition could not provide a curing product having satisfactory heat resistance, electrical properties, and dimensional stability.
Examples of another resin composition include resin compositions containing a polyimide resin. Examples of the resin composition containing a polyimide resin include a thermosetting polyimide resin composition containing a polyimide resin which has a carboxyl group and a linear hydrocarbon structure having a number average molecular weight of 300 to 6,000, and an epoxy resin (for example, see Patent document No. 2). However, the thermosetting polyimide resin composition could not provide a cured material which had sufficient heat resistance and dimensional stability.    [Patent document No. 1] Japanese Unexamined Patent Application, First Publication No. H5-295090    [Patent document No. 2] Japanese Unexamined Patent Application, First Publication No. 2003-292575